eeprom/at25: bugfix "not ready" timeout after write

Under certain circumstances msleep(1) within the loop, which waits for the
EEPROM to be finished, might take longer than the timeout.  On the next
loop the status register might now return to be ready and therefore the
loop finishes.  The following check now tests if a timeout occurred and if
so returns an error although the device reported it was ready.

This fix replaces testing the occurrence of the timeout by testing the
"not ready" bit in the status register.

Signed-off-by: Sebastian Heutling <heutling@who-ing.de>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>