docs: Fix case of Cypress readme file

Fix the case of the cypress readme to fix dead links in the docs.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/README.md b/README.md
index 8007b2c..51926b9 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@
 - [RIOT](docs/readme-riot.md)
 - [Mbed OS](docs/readme-mbed.md)
 - [Espressif](docs/readme-espressif.md)
-- [Cypress/Infineon](boot/cypress/readme.md)
+- [Cypress/Infineon](boot/cypress/README.md)
 
 There are also instructions for the [Simulator](sim/README.rst).