PCI: Remove sysfs resource mmap warning

When a process uses sysfs and tries to mmap more space than is available in
a PCI BAR, we emit a warning and a backtrace.  The mmap fails anyway, so
the backtrace is mainly for debugging.  But in general we don't emit kernel
messages when syscalls return failure.

The similar procfs mmap path simply fails the mmap with no warning.  Remove
the sysfs warning.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>