Both tmp_count computations and the single use can be eliminated using
min(). Do so.

Side note: we need HEADER_SIZE to be unsigned for min() not to complain.
Fix that too as all its other uses do not mind.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200818085706.12163-11-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>