scripts/spelling.txt: add regsiter -> register spelling mistake

This typo is quite common.  Fix it and add it to the spelling file so
that checkpatch catches it earlier.

Link: http://lkml.kernel.org/r/20170317011131.6881-2-sboyd@codeaurora.org
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/cpufreq/sti-cpufreq.c b/drivers/cpufreq/sti-cpufreq.c
index a7db901..d2d0430 100644
--- a/drivers/cpufreq/sti-cpufreq.c
+++ b/drivers/cpufreq/sti-cpufreq.c
@@ -236,7 +236,7 @@
 	return 0;
 }
 
-static int sti_cpufreq_fetch_syscon_regsiters(void)
+static int sti_cpufreq_fetch_syscon_registers(void)
 {
 	struct device *dev = ddata.cpu;
 	struct device_node *np = dev->of_node;
@@ -275,7 +275,7 @@
 		goto skip_voltage_scaling;
 	}
 
-	ret = sti_cpufreq_fetch_syscon_regsiters();
+	ret = sti_cpufreq_fetch_syscon_registers();
 	if (ret)
 		goto skip_voltage_scaling;