misc: fastrpc: fix indentation error in uapi header

Use tabs instead of spaces.

Fixes: 2419e55e ("misc: fastrpc: add mmap/unmap support")
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20200908131013.19630-2-jonathan@marek.caSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>