parisc: Use parentheses around expression in floppy.h

David Binderman reported a style issue in the floppy.h header file:
arch/parisc/include/asm/floppy.h:221: (style) Boolean result is used in bitwise
  operation. Clarify expression with parentheses.

Reported-by: David Binderman <dcb314@hotmail.com>
Cc: David Binderman <dcb314@hotmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>