bcma: remove unused mips_read32 function

clang with W=1 reports
drivers/bcma/driver_mips.c:49:19: error: unused function
  'mips_read32' [-Werror,-Wunused-function]
static inline u32 mips_read32(struct bcma_drv_mips *mcore,
                  ^
This function is not used so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230324190647.2654293-1-trix@redhat.com