fs: fat: remove trailing periods from long name

The FAT32 File System Specification [1] requires leading and trailing
spaces as well as trailing periods of long names to be ignored.

[1]
    Microsoft Extensible Firmware Initiative
    FAT32 File System Specification
    Version 1.03, December 6, 2000
    Microsoft Corporation
    https://www.win.tue.nl/~aeb/linux/fs/fat/fatgen103.pdf



Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>