Fix a one-character typo at the makefile.

drivers/built-in.o: In function `flexcop_pci_remove':
flexcop-pci.c:(.text+0x20d1a28): undefined reference to `flexcop_dma_free'
flexcop-pci.c:(.text+0x20d1a3e): undefined reference to `flexcop_dma_free'
drivers/built-in.o: In function `flexcop_pci_stream_control':
flexcop-pci.c:(.text+0x20d2396): undefined reference to `flexcop_dma_config'
flexcop-pci.c:(.text+0x20d23b3): undefined reference to `flexcop_dma_config'
flexcop-pci.c:(.text+0x20d23cf): undefined reference to `flexcop_dma_config_timer'
flexcop-pci.c:(.text+0x20d23f5): undefined reference to `flexcop_dma_xfer_control'
flexcop-pci.c:(.text+0x20d244c): undefined reference to `flexcop_dma_control_timer_irq'
flexcop-pci.c:(.text+0x20d24b0): undefined reference to `flexcop_dma_control_timer_irq'
flexcop-pci.c:(.text+0x20d2507): undefined reference to `flexcop_dma_xfer_control'
drivers/built-in.o: In function `flexcop_pci_probe':
flexcop-pci.c:(.text+0x20d28d2): undefined reference to `flexcop_dma_allocate'
flexcop-pci.c:(.text+0x20d2907): undefined reference to `flexcop_dma_allocate'
flexcop-pci.c:(.text+0x20d2923): undefined reference to `flexcop_dma_free'
Reported-by: NFengguang Wu <wfg@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>