staging: rts5208: remove unused xd_check_err_code function

staging: rts5208: remove unused xd_check_err_code function

clang with W=1 reports
drivers/staging/rts5208/xd.c:34:19: error: unused function
  'xd_check_err_code' [-Werror,-Wunused-function]
static inline int xd_check_err_code(struct rtsx_chip *chip, u8 err_code)
                  ^
This function is not used, so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230321190127.1827703-1-trix@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>