mmc: core: Correct misspelling of 'mq' in mmc_init_request()'s docs

mmc: core: Correct misspelling of 'mq' in mmc_init_request()'s docs

Correcting this misspelling squashes the following W=1 build warning(s):

 mmc/core/queue.c:212: warning: Function parameter or member 'mq' not described in '__mmc_init_request'
 mmc/core/queue.c:212: warning: Excess function parameter 'q' description in '__mmc_init_request'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200701124702.908713-8-lee.jones@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>