mmc: fix compiler warnings

Commit d2bf29e3 caused a number of compiler warnings:

mmc.c: In function 'mmc_bwrite':
mmc.c:97: warning: format '%x' expects type 'unsigned int', but argument 2 has type 'long unsigned int'
mmc.c:97: warning: format '%x' expects type 'unsigned int', but argument 3 has type 'lbaint_t'
mmc.c: In function 'mmc_bread':
mmc.c:229: warning: format '%x' expects type 'unsigned int', but argument 2 has type 'long unsigned int'
mmc.c:229: warning: format '%x' expects type 'unsigned int', but argument 3 has type 'lbaint_t'

Fix these.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Lei Wen <leiwen@marvell.com>