firmware: arm_scpi: Prevent the ternary sign expansion bug

firmware: arm_scpi: Prevent the ternary sign expansion bug

How the type promotion works in ternary expressions is a bit tricky.
The problem is that scpi_clk_get_val() returns longs, "ret" is a int
which holds a negative error code, and le32_to_cpu() is an unsigned int.
We want the negative error code to be cast to a negative long.  But
because le32_to_cpu() is an u32 then "ret" is type promoted to u32 and
becomes a high positive and then it is promoted to long and it is still
a high positive value.

Fix this by getting rid of the ternary.

Link: https://lore.kernel.org/r/YIE7pdqV/h10tEAK@mwanda
Fixes: 8cb7cf56c9fe ("firmware: add support for ARM System Control and Power Interface(SCPI) protocol")
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[sudeep.holla: changed to return 0 as clock rate on error]
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>