hw/net/e1000e: Fix compiler warning

slave:~/.xie/qemu-colo # gcc --version
gcc (SUSE Linux) 4.3.4 [gcc-4_3-branch revision 152973]

slave:~/.xie/qemu-colo # make -j8
CC    hw/net/e1000e_core.o
hw/net/e1000e_core.c:56: warning: ‘e1000e_set_interrupt_cause’ declared inline after being called
hw/net/e1000e_core.c:56: warning: previous declaration of ‘e1000e_set_interrupt_cause’ was here
LINK  x86_64-softmmu/qemu-system-x86_64
Signed-off-by: NChanglong Xie <xiecl.fnst@cn.fujitsu.com>
Reviewed-by: NDmitry Fleytman <dmitry@daynix.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/net/e1000e_core.c

@@ -52,7 +52,7 @@
                                      second according to spec 10.2.4.2 */
 #define E1000E_MAX_TX_FRAGS (64)
 
-static void
+static inline void
 e1000e_set_interrupt_cause(E1000ECore *core, uint32_t val);
 
 static inline void