spi: cadence-quadspi: Fix build warning on 32-bit platforms

spi: cadence-quadspi: Fix build warning on 32-bit platforms

The kernel test robot reports the following warning.

drivers/spi/spi-cadence-quadspi.c:966:24: warning: comparison of distinct pointer types ('typeof (len) *' (aka 'unsigned int *') and 'typeof (500UL) *' (aka 'unsigned long *')) [-Wcompare-distinct-pointer-types]
                                            msecs_to_jiffies(max(len, 500UL)))) {
                                                             ^~~~~~~~~~~~~~~
   include/linux/minmax.h:58:19: note: expanded from macro 'max'
   #define max(x, y)       __careful_cmp(x, y, >)
                           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/minmax.h:42:24: note: expanded from macro '__careful_cmp'
           __builtin_choose_expr(__safe_cmp(x, y), \
                                 ^~~~~~~~~~~~~~~~
   include/linux/minmax.h:32:4: note: expanded from macro '__safe_cmp'
                   (__typecheck(x, y) && __no_side_effects(x, y))
                    ^~~~~~~~~~~~~~~~~
   include/linux/minmax.h:18:28: note: expanded from macro '__typecheck'
           (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                      ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
   1 warning generated.

This happens because size_t is unsigned long on 64-bit platforms like
arm64 but it is unsigned int on 32-bit platforms like arm. Omitting the
"UL" would result in a warning on 64-bit platforms. Squash it by type
casting the arguments to size_t using max_t(). This way builds on both
type of platforms can be satisfied. There is no chance of any truncation
since 500 is small enough to fit into both int and long.

Fixes: f453f293979f ("spi: cadence-quadspi: Wait at least 500 ms for direct reads")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20210108181457.30291-1-p.yadav@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>