rtl8139: Remove unused variable

rtl8139: Remove unused variable

Variable send_count used in rtl8139_cplus_transmit_one function is only
incremented but never read. This causes 'Unused but set variable' warning
on Clang 15.0.1 compiler.

Removing the variable to prevent the warning.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <15a32dd06c492216cbf27cd3ddcbe1e9afb8d8f5.1668009030.git.mrezanin@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 7d7238c72b983cff5064734349d2d45be9c6282c)