Fix the bitmasks used when writing to the M41T00 registers.

The original code used a mask of 0x7f when writing to each register,
this is incorrect and probably the result of a copy-paste error.  As a
result years from 1980 to 1999 will be read back as 2000 to 2019.

Signed-off-by: David Barksdale <amatus@ocgnet.org>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>