Revert "fb: Initialize fb_info mutexes in framebuffer_alloc()"

This reverts commit 4148df9b.

Let's hope that the mm_lock initialization is now correct with all
drivers, following Krzysztof's patches.

Requested-by: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>