mmc: sdhci-brcmstb: Fix compiler warning

Fix the compiler warning triggered by -Wmissing-prototypes for
brcmstb_reset() by making it static.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20220506082805.273909-1-ulf.hansson@linaro.org

drivers/mmc/host/sdhci-brcmstb.c

@@ -48,7 +48,7 @@ static inline void enable_clock_gating(struct sdhci_host *host)
 	sdhci_writel(host, reg, SDHCI_VENDOR);
 }
 
-void brcmstb_reset(struct sdhci_host *host, u8 mask)
+static void brcmstb_reset(struct sdhci_host *host, u8 mask)
 {
 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
 	struct sdhci_brcmstb_priv *priv = sdhci_pltfm_priv(pltfm_host);