mmc: card: fixing an false identification of SANITIZE command

Inside the routine mmc_blk_ioctl_cmd() the sanitize command is
identified according to the value of bits 16-23 of the argument.

but what happens if a different command is sent, and only by
chance, bits 16-23 contain the value of SANITIZE command ?
In that case a SANITIZE command will be falsely identified.
In order to prevent such a case, the condition is expanded and
now it also checks the opcode itself, and verifies that it is an
MMC_SWITCH opcode.

Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
Signed-off-by: Chris Ball <cjb@laptop.org>